This invention relates to the provision of molded plastic caps adapted to be screwed onto the threaded neck of a container to seal the same when not in use.
The increasing popularity of plastic containers and plastic caps used therewith, most particularly gallon-size containers used for milk, fruit drinks, distilled or mineral water, anti-freeze and a number of other products, has given rise to the requirement for tamper-proof caps which lock onto the container when first applied during the packaging of the contained product and which cannot be removed without producing some visible change in the appearance of the cap.
To this end, the plastic containers are conventionally formed with retainer means, such as ratchet teeth, surrounding the neck of the container below the external threads onto which the threaded cap is screwed. The internally-threaded cap is provided with a lower skirt which is releasably attached to the main cap body and which is provided with internal engagement means which are adapted to slip over the ratchet teeth and engage the same when the cap is screwed onto the container in a clockwise direction to seal the same. However, the cap cannot be unscrewed from the container without some change occurring in the appearance thereof.
Most such safety caps are injection molded with releasably-attached skirts having inwardly-projecting angular or slanted teeth which are designed to slip over the bottle neck ratchet when the cap is screwed onto the container but which resist reverse-rotation. Reference is made to U.S. Pat. Nos. 3,902,621 and 3,980,195 which disclose caps of this type on which the retainer skirt is provided with a pull-tab and is adapted to be pulled away from the cap to remove the locking means and adapt the cap to be freely unscrewed from the container. Such a pull-tab arrangement is effective for its intended purpose but has the disadvantage that it requires an operation, separate from the unscrewing operation, to permit the latter operation to be accomplished. Also, the removal of the pull-tab requires finger-tip strength and can result in breakage of the pull-tab and inconvenience to the user.
Reference is also made to U.S. Pat. Nos. 3,504,818 and 3,874,540 as representative of injection-molded safety caps having engagement skirts which are adapted to break away from the main cap during the initial removal of the cap from the container. Such caps do not require a separate operation to disengage the skirt but they do have the disadvantage of requiring sufficient applied strength to cause the retainer skirt to break away from the main cap before the main cap will unscrew. Such strength is not possessed by a large segment of the consuming public, such as senior citizens and children.
Another disadvantage of molded safety caps with break-away retainer skirts results from the narrow breakable connectors which extend outwardly from the main cap body to the skirt. When such connectors break, they can leave sharp remnants on the periphery of the cap, which remnants can cause pain and injury to delicate fingertips each time the cap is grasped to seal or unseal the container.
It is also known to produce tamper-proof caps by thermoforming techniques and to provide the retainer skirt with one or more tabs which project downwardly or inwardly from the skirt element, in a counterclockwise direction, so as to ride over and engage the ratchet retainer on the bottle neck when the cap is applied to the neck by clockwise rotation. Since the tabs have the same thickness as the remainder of the thermoformed cap and are attached thereto by means of a narrow hinge line, such tabs offer little resistance to the removal of the cap and thus provide advantages over other safety caps. However, the small tabs break away from the retainer skirt during initial removal of the cap and can fall into the container when the cap is lifted from the container or can remain on the neck of the container and fall into a glass or other receptacle into which the product is poured from the container.